Construction of a ternary system: a strategy for the rapid formation of porous poly(lactic acid) fibers

Combining electrospinning technology with nonsolvent induced phase separation (ESP-NIPS), 10 wt% poly(lactic acid) (PLA) spinning solutions are prepared by using chloroform as a good solvent and absolute ethanol as a nonsolvent. The “PLA/CHCl₃/C₂H₅OH” ternary system is constituted to realize the rapid preparation of porous-structured PLA fibers. The morphologies, thermal properties and crystalline structures of the obtained fibers are characterized and the rapid forming mechanism of PLA porous fibers is investigated and discussed. The interaction parameters between the substances of the “PLA/CHCl₃/C₂H₅OH” ternary system, binodal line, spinodal line and critical point are obtained by theoretical calculation and experiment, and the “PLA/CHCl₃/C₂H₅OH” ternary phase diagram model is established. The results show that, when the mass ratio of chloroform/ethanol is around 75/25, the rapid “in situ” formation of the PLA fibers can be realized with porous structures within 5–10 s. The establishment of a “nonsolvent-solvent–polymer” ternary phase diagram model has laid a theoretical foundation for the rapid formation of polymer porous fibers by ESP-NIPS. The ESP-NIPS for the porous PLA fibers preparation provides a new resolution for the rapid formation of porous polymer materials, which is vital to further expand the application of electrospun fibers in emergency situations such as isolation, protection, insulation and flame retardant usage.

Combining electrospinning technology with ESP-NIPS, using chloroform as a solvent and absolute ethanol as a nonsolvent, poly(lactic acid) porous fibres are prepared within 5–10 s. This preparation provides a new resolution for the rapid formation of porous polymer materials.     

Nuclear quantum effect and H/D isotope effect on Cl· + (H2O)n → HCl + OH·(H2O)n−1 (n = 1–3) reactions

Cl· + (H₂O)_n → HCl + OH·(H₂O)_n−1 (n = 1–3) reactions are fundamental and important ones in atmospheric chemistry. In this study, we focused on the nuclear quantum effect (NQE) of the hydrogen nucleus on these reactions with the aid of the multicomponent quantum mechanics (MC_QM) method, which can directly take account of NQE of light nuclei. Our study reveals that the NQE of the hydrogen nucleus lowers the activation barriers of the reactions and enhances the catalytic effects of second and third water molecules. In particular, we find that (i) the NQE of the proton removes the activation barrier of the reverse reaction of HCl + OH· → Cl· + H₂O, and (ii) the catalytic effect of the third water molecule appears in only our MC_QM calculation. We also analyze the H/D isotope effects on these reactions by using the MC_QM method.

Cl·+ (H₂O)_n → HCl + OH(H₂O)_n−1 (n = 1–3) reactions have been investigated using multicomponent quantum mechanics method, which can take account of the nuclear quantum effect of proton and deuteron.     

Photophysical properties and singlet oxygen generation of meso-iodinated free-base corroles

In order to study the effect of meso-iodination of free-base corroles on their photophysical character, we designed and synthesized a series of free-base corrole derivatives F10–OH (iodine-free), F10–OH–I (mono-iodo) and F10–OH–2I (di-iodo), with different substitution patterns at the meso-position as candidates for photodynamic therapy (PDT). We employed several optical spectroscopic techniques, including time-resolved spectroscopy from a femtosecond to microsecond and singlet oxygen luminescence to study the properties of excited singlet and triplet states, as well as the singlet oxygen quantum yields. The sub-picosecond internal conversion, ∼1 ps intramolecular vibrational energy redistribution, tens of ps vibrational cooling, are similar across the three corroles. The addition of one (F10–OH–I) and two iodine (F10–OH–2I) atoms to the remote aryl ring of triarylcorroles induces a 4.6-fold and 6.2-fold decrease in fluorescence quantum yields Φ_fl and a 2.2-fold and 4.9-fold increase in the time constant of intersystem crossing k_ISC. In addition, a slight increase in intersystem crossing quantum yields Φ_T was also observed from F10–OH to F10–OH–2I. It means the intersystem crossing is improved by the iodination, from F10–OH to F10–OH–2I, because of the heavy atom effect. However, the sample F10–OH–I, instead of F10–OH–2I, shows the highest singlet oxygen quantum yield Φ_Δ.

The effect of corrole macrocycle meso-iodination on its photophysical character.     

Zirconium-based metal–organic framework gels for selective luminescence sensing

Metal–organic gelation represents a promising approach to fabricate functional nanomaterials. Herein a series of Zr-carboxylate gels are synthesized from rigid pyrene, porphyrin and tetraphenyl ethylene-derived tetracarboxylate linkers, namely Zr-TBAPy (H₄TBAPy = 1,3,6,8-tetrakis(4-carboxylphenyl)pyrene), Zr-TCPE (H₄TCPE = 1,1,2,2-tetra(4-carboxylphenyl)ethylene), and Zr-TCPP (H₄TCPP = 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin). The gels are aggregated from metal–organic framework (MOF) nanoparticles. Zr-TBAPy gel consists of NU-901 nanoparticles, and Zr-TCPP gel consists of PCN-224 nanoparticles. The xerogels show high surface areas up to 1203 m² g⁻¹. MOF gel films are also anchored on the butterfly wing template to yield Zr-MOF/B composites. Zr-TBAPy and Zr-TCPE gels are luminescent for solution-phase sensing and vapour-phase sensing of volatile organic compounds, and exhibit a significant luminescence quenching effect for electron-deficient analytes. Arising from the high porosity and good dispersion of luminescent MOF gels, rapid and effective vapour-sensing of nitrobenzene and 2-nitrotoluene within 30 s has been achieved via Zr-TBAPy film or Zr-TBAPy/B.

Zr-based MOF nanomaterials are developed via a metal–organic gelation method for rapid and effective luminescence vapour-sensing.     

One-pot facile simultaneous in situ synthesis of conductive Ag–polyaniline composites using Keggin and Preyssler-type phosphotungstates

Two heteropolytungstate structures, Keggin (H₃PW₁₂O₄₀) and Preyssler (H₁₄[NaP₅W₃₀O₁₁₀]), were used to synthesize conductive silver nanoparticle–polyaniline–heteropolytungstate (AgNPs–PAni–HPW) nanocomposites. During the oxidative polymerization of aniline, heteropolyblue was generated and served as the reducing agent to stabilize and distribute AgNPs within “PAni–Keggin” and “PAni–Preyssler” matrixes as well as on their surfaces. The prepared nanocomposites and AgNPs were characterized using UV-visible (UV-Vis) and Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), pore size distribution BET, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). UV-Vis results showed different stages of the formation of metal NPs embedded in the polymer–HPW composites, and FT-IR spectra presented characteristic bands of PAni, Keggin and Preyssler anions in the composites confirming no changes in their structures. The presence of AgNPs and an intensely crystalline matrix were confirmed by the XRD pattern. The BET surface areas were found to be 38.426 m² g⁻¹ for “AgNPs–PAni–Keggin” and 29.977 m² g⁻¹ for “AgNPs–PAni–Preyssler” nanocomposites with broad distributions of meso-porous structure for both nanocomposites. TEM and SEM images confirmed that the type of heteropolyacids affected the size of AgNPs. This is the first report that uses Keggin and Preyssler-type heteropolytungstate to synthesize “AgNPs–PAni–HPW” nanocomposites in an ambient condition through a low-cost, facile, one-pot, environmentally friendly and simultaneous in situ oxidative polymerization protocol.

Two heteropolytungstate structures, (a) Keggin (H₃PW₁₂O₄₀) and (b) Preyssler (H₁₄(NaP₅W₃₀O₁₁₀]), have been used to synthesize conductive silver nanoparticle–polyaniline–heteropolytungstate, (AgNPs–PAni–HPW) nanocomposites.     

Novel polymeric acidic ionic liquids as green catalysts for the preparation of polyoxymethylene dimethyl ethers from the acetalation of methylal with trioxane

A series of micro–mesoporous polymeric acidic ionic liquids (PAILs) have been successfully synthesized and subsequently characterized using Fourier transform-infrared spectroscopy, N₂ adsorption–desorption isotherms, scanning electron microscopy and thermogravimetry. Furthermore, the catalytic performance of the synthesized PAILs was investigated for the acetalation of methylal (DMM₁) with 1,3,5-trioxane (TOX), micro–mesoporous PAILs copolymerized by divinylbenzene with cations and anions exhibited moderate to excellent catalytic activities for the acetalation. In particular, VIMBs–AMPs–DVB, with higher specific surface area (25.51 m² g⁻¹) and total pore volume (0.15 cm³ g⁻¹) displayed an elevated conversion of formaldehyde (82.2%) and selectivity for polyoxymethylene dimethyl ethers (CH₃O(CH₂O)_nCH₃; PODE_n or DMM_n) n = 3–8 (52.6%) at 130 °C, 3.0 MPa for 8 h. Moreover, the influence of various reaction parameters was investigated by employing VIMBs–AMPs–DVB as the catalyst and it demonstrated high thermal stability and easy recovery.

Polyoxymethylene dimethyl ethers were successfully synthesized from acetalation under the catalysis of novel polymeric acidic ionic liquids (PAILs). PAILs copolymerized by divinylbenzene with ILs displayed exceptional catalytic efficiencies.     

Syntheses,structures, and magnetic properties of mixed-ligand complexes based on 3,6-bis(benzimidazol-1-yl)pyridazine

Six new metal–organic coordination polymers (CPs) [Ni(L)(2,5-TDC)(H₂O)]_n(1), [Ni(L)(1,3-BDC)(H₂O)]_n (2), [Ni(L)(1,4-BDC)(H₂O)]_n (3), [Mn(L)(2,5-TDC)(H₂O)]_n (4), [Mn(L)(2,6-PYDC)(H₂O)]_n (5) and [Mn(L)(1,4-NDC)]_n (6) were achieved by reactions of the corresponding metal salt with mixed organic ligands (L = 3,6-bis(benzimidazol-1-yl)pyridazine, 2,5-H₂TDC = thiophene-2,5-dicarboxylic acid, 1,3-H₂BDC = isophthalic acid, 1,4-H₂BDC = terephthalic acid, 2,6-H₂PYDC = pyridine-2,6-dicarboxylic acid, 1,4-H₂NDC = naphthalene-1,4-dicarboxylic acid) under solvothermal condition. CPs 1–6 were characterized by single-crystal X-ray diffraction, IR, TG, XRD and elemental analyses. Their structures range from the intricate 3D CPs 1, 3, 4 and 6 to the 2D coordination polymer 2 and the infinite 1D chain 5. The CPs 1–4 and 6 underlying networks were classified from the topological viewpoint, disclosing the distinct sql (in 1), pcu (in 3 and 6), new topology (in 2), and dia (in 4) topological nets. Moreover, analysis of thermal stability shows that they had good thermal stability. Finally, magnetic properties of CPs 1–6 have been studied, the results showed that complex 2 had ferromagnetic coupling and complexes 1, 3–6 were antiferromagnetic.

Six new metal–organic coordination polymers were prepared by reactions of the corresponding metal salt with mixed organic ligands under solvothermal conditions. The compounds were structurally, magnetically and catalytically characterized.     

Synthesis and characterization of MOFs constructed from 5-(benzimidazole-1-yl)isophthalic acid and highly selective fluorescence detection of Fe(iii) and Cr(vi) in water

In this work, four novel metal–organic frameworks [Cd(bipa)]_n (1), {[Zn₂(bipa)₂]·2C₂H₅OH}_n (2), {[Co(bipa)]·C₂H₅OH}_n (3), {[Ni(bipa)₂]·2DMA}_n (4), (H₂bipa = 5-(benzimidazole-1-yl)isophthalic acid) were successfully synthesized under solvothermal conditions. Complexes 1–4 were characterized by powder X-ray diffraction, elemental analysis, infrared spectroscopy and thermogravimetric analysis. Interestingly, the coordination patterns and 3D network structures of complexes 1–3 are very similar, while complex 4 is relatively unique. Complexes 1–2 exhibit potential fluorescent properties. Complex 1 can selectively and sensitively detect trace Fe(iii) and Cr(vi) in water by fluorescence quenching detection, and the quenching mechanism is further discussed.

In this work, four novel MOFs [Cd(bipa)]_n (1), {[Zn₂(bipa)₂]·2C₂H₅OH}_n (2), {[Co(bipa)]·C₂H₅OH}_n (3), {[Ni(bipa)₂]·2DMA}_n (4), (H₂bipa = 5-(benzimidazole-1-yl)isophthalic acid) were successfully synthesized under solvothermal conditions.     

A novel fluorescence phenomenon caused by amine induced ion-exchange between Cd2+ and Fe3+ ions

A 3D metal–organic framework {[Cd(5-Brp)(dpa)]·0.5DMF·H₂O}_n (1) was successfully synthesized and characterized, which markedly recognized iron ions under the induction of an amino group. With the concentration of Fe³⁺ increasing, the emission of 1 first declined, then enhanced with a red shift and was finally quenched, which was different from the reference compound [Cd(5-Brp)(bpp)(H₂O)]_n (2). This result drew our attention to amine induced ion-exchange. This peculiar phenomenon inspired us to construct an effective ion detector.

A 3D metal–organic framework {[Cd(5-Brp)(dpa)]·0.5DMF·H₂O}_n (1) was successfully synthesized and characterized, which markedly recognized iron ions under the induction of an amino group.     

Efficiency of liquid tin(ii) n-alkoxide initiators in the ring-opening polymerization of l-lactide: kinetic studies by non-isothermal differential scanning calorimetry

Novel soluble liquid tin(ii) n-butoxide (Sn(OnC₄H₉)₂), tin(ii) n-hexoxide (Sn(OnC₆H₁₃)₂), and tin(ii) n-octoxide (Sn(OnC₈H₁₇)₂) initiators were synthesized for use as coordination–insertion initiators in the bulk ring-opening polymerization (ROP) of l-lactide (LLA). In order to compare their efficiencies with the more commonly used tin(ii) 2-ethylhexanoate (stannous octoate, Sn(Oct)₂) and conventional tin(ii) octoate/n-alcohol (SnOct₂/nROH) initiating systems, kinetic parameters derived from monomer conversion data were obtained from non-isothermal differential scanning calorimetry (DSC). In this work, the three non-isothermal DSC kinetic approaches including dynamic (Kissinger, Flynn–Wall, and Ozawa); isoconversional (Friedman, Kissinger–Akahira–Sunose (KAS) and Ozawa–Flynn–Wall (OFW)); and Borchardt and Daniels (B/D) methods of data analysis were compared. The kinetic results showed that, under the same conditions, the rate of polymerization for the 7 initiators/initiating systems was in the order of liquid Sn(OnC₄H₉)₂ > Sn(Oct)₂/nC₄H₉OH > Sn(Oct)₂ ≅ liquid Sn(OnC₆H₁₃)₂ > Sn(Oct)₂/nC₆H₁₃OH ≅ liquid Sn(OnC₈H₁₇)₂ > Sn(Oct)₂/nC₈H₁₇OH. The lowest activation energies (E_a = 52, 59, and 56 kJ mol⁻¹ for the Kissinger, Flynn–Wall, and Ozawa dynamic methods; E_a = 53–60, 55–58, and 60–62 kJ mol⁻¹ for the Friedman, KAS, and OFW isoconversional methods; and E_a = 76–84 kJ mol⁻¹ for the B/D) were found in the polymerizations using the novel liquid Sn(OnC₄H₉)₂ as the initiator, thereby showing it to be the most efficient initiator in the ROP of l-lactide.

The efficiency of homogeneous liquid tin(ii) n-alkoxide initiators in the ROP of l-lactide was reported in this work by non-isothermal DSC kinetic approaches.     

Supramolecular organogels fabricated with dicarboxylic acids and primary alkyl amines: controllable self-assembled structures

Supramolecular organogels are soft materials comprised of low-molecular-mass organic gelators (LMOGs) and organic liquids. Owning to their unique supramolecular structures and potential applications, LMOGs have attracted wide attention from chemists and biochemists. A new “superorganogel” system based on dicarboxylic acids and primary alkyl amines (R–NH₂) from the formation of organogels is achieved in various organic media including strong and weak polar solvents. The gelation properties of these gelators strongly rely on the molecular structure. Their aggregation morphology in the as-obtained organogels can be controlled by the solvent polarity and the tail chain length of R–NH₂. Interestingly, flower-like self-assemblies can be obtained in organic solvents with medium polarity, such as tetrahydrofuran, pyridine and dichloromethane, when the gelators possess a suitable length of carbon chain. Moreover, further analyses of Fourier transformation infrared spectroscopy and ¹H nuclear magnetic resonance spectroscopy reveal that the intermolecular acid–base interaction and van der Waals interaction are critical driving forces in the process of organogelation. In addition, this kind of organogel system displays excellent mechanical properties and thermo-reversibility, and its forming mechanism is also proposed.

A new kind of supramolecular organogel system based on dicarboxylic acids and primary alkyl amines (R–NH₂) was obtained, in which the aggregation morphology of gelators could be controlled by solvent polarity and tail chain length.     

A stable LnMOF as a highly efficient and selective luminescent sensor for detecting malachite green in water and real samples

A series of isostructural 3D lanthanide metal–organic frameworks (LnMOFs), with the formula n(H₃O)[Ln(L)(H₂O)]_n·nH₂O (Ln = Gd 1, Eu 2 and Tb 3, H₄L = 3,5,3′,5′-oxytetrabenzoic acid), have been successfully synthesized by solvothermal reactions. Single-crystal X-ray diffraction analysis reveals that 1–3 are constructed from wave-like Ln–carboxylate chains which are further connected by the ligands to form 3D channel-type frameworks. Further experiments suggest that 3 is thermally stable up to 322 °C and exhibits outstanding chemical stability in aqueous solutions with the pH ranging from 3 to 11. Significantly, 3 can be utilized for the first time to detect malachite green (a synthetic antibiotic to cure saprolegniasis) in aqueous media even in the presence of other interfering antibiotics, with a high sensitivity (K_sv = 8.33 × 10⁴ M⁻¹), low detection limit (DL = 0.25 μM) and good recyclability. On a more practical note, we found that the luminescence intensity of 3 showed almost no response to pH changes (pH 3–11), allowing steady sensing in real samples such as river water, simulated human serum and urine with satisfactory recoveries and RSD.

A Tb-MOF with chemical stability was synthesized. It showed excellent luminescent sensing for MG in river water, simulated serum and urine.     

Photochromic properties of three 2D MOFs based on 1-carboxyethyl-4,4′-bipyridinine

Viologen units have been widely used to impart metal–organic frameworks (MOFs) with photochromic properties. However, construction of a stable photochromic system in viologen MOFs has not been fully explored. Herein, we report three examples of MOFs, namely, {[Cd(CEbpy)(m-BDC)(DMF)]·2H₂O}_n (1), {[Cd(CEbpy)(p-BDC)(H₂O)]·H₂O}_n (2), and {[Zn(CEbpy)(p-HBDC)(p-BDC)_0.5]·H₂O}_n (3) based on benzenedicarboxylic acids (m-H₂BDC = 1,3-benzenedicarboxylic acid, p-H₂BDC = 1,4-benzenedicarboxylic acid) and a viologen-derived ligand 1-carboxyethyl-4,4′-bipyridine (L = CEbpy). As expected, the incorporation of the viologen unit into the frameworks results in the predefined photochromism upon both sunlight and UV-light. Compounds 1–3 feature a two-dimensional (2D) layered structure and are all photochromic due to the formation of CEbpy radicals by photoinduced electron transfer (PET). The aggregates build an interesting stable crystalline framework that exhibits long-lived color constancy in the solid state.

Viologen units have been widely used to impart metal–organic frameworks (MOFs) with photochromic properties.     

Effects of template molecules on the structures and luminescence intensities of a series of porous Tb-MOFs based on the 2-nitroterephthalate ligand

Four novel porous Tb(iii) metal–organic frameworks (Tb-MOFs) have been designed and prepared hydrothermally from 2-nitroterephthalate (2-H₂ntp), namely {[Tb(2-ntp)_1.5(H₂O)]·H₂O}_n (1), {[Tb(2-ntp)₂(H₂O)]·4,4′-Hbipy}_n (2), {[Tb(2-ntp)₂(H₂O)]·2,4-Hbipy}_n (3), and {[Tb(2-ntp)₂(H₂O)]·(1,4-H₂bbi)_0.5}_n (4) (4,4′-bipy = 4,4′-bipyridine; 2,4-bipy = 2,4-bipyridine; 1,4-bbi = 1,4-bisbenzimidazole). X-ray diffraction structural analyses show these Tb-MOFs are porous and are based on Tb³⁺ ions and 2-nitroterephthalate, in which water molecules (1) or protonated N-donor ligands (2–4) exist as templates. The fluorescence properties of complexes 1–4 could be associated with the characteristic peaks of Tb(iii) ions, and the existence of different guest molecules affects the intensities of peaks, which means that these could be potential fluorescence materials, with intensities adjusted using guests.

Four porous Tb-MOFs based on 2-nitroterephthalate are described, in whose pores water (1) or co-ligands (2–4) exist in the pores as templates. The emissions could be related to the characteristic peaks of Tb(iii) ions, and their intensities are affected and adjusted by templates.     

Non-scrambling of hydrogen in NH4+(H2O)3 clusters

We have measured the metastable decay of protonated, ammonia-doped, deuterated water clusters produced in an electrospray source, d_n-NH₄⁺(H₂O)₃, n = 0–6. The mass spectra show a very strong odd–even effect, consistent with a low degree of scrambling of the hydrogen bound to water and to the ammonia. The relative evaporation rate constant for light water was almost twice the one for heavy water, with the rate for mixed protium–deuterium water molecule intermediate between these two values.

We have measured the metastable decay of protonated, ammonia-doped, deuterated water clusters produced in an electrospray source, d_n-NH₄⁺(H₂O)₃, n = 0–6.     

A stable Ln(iii)-functionalized Cd(ii)-based metal–organic framework: tunable white-light emission and fluorescent probe for monitoring bilirubin

A novel anionic Cd(ii)-based metal–organic framework, H₂[Cd₉(DDB)₄(BPP)₄(H₂O)₁₄]·4H₂O·2DMA (1), was successfully obtained with a rigid carboxylate ligand 3,5-di(2′,4′-dicarboxylphenyl)benzoic acid (H₅DDB) and a flexible pyridyl ligand 1,3-bis(4-pyridyl)propane (BPP). Complex 1 contains two-dimensional (2D) honeycomb structures and one-dimensional (1D) chain structures. The adjacent 2D structures are linked by strong intermolecular hydrogen bonds to form an ABAB 3D supramolecular structure, where the 1D chain structures traverse the channels of the 2D structures. Due to the anionic framework, Ln(iii) ions (Ln = Eu and Tb) can be encapsulated in the framework of 1 by a post-synthetic modification process to obtain Ln(iii)@1, where 1.09Eu(iii)@1 (1a) and 0.658Tb(iii)@1 (1b) can be obtained by soaking complex 1 in a Eu(NO₃)₃·6H₂O or Tb(NO₃)₃·6H₂O aqueous solution for 48 h. The liquid-state emission spectra of Ln(iii)@1 can be tuned to be a white light emission by changing the Eu(iii)/Tb(iii) molar ratio in solution. Moreover, 1b can be used as a “turn-off” fluorescent probe for bilirubin with a low detection limit of 0.250 μM in phosphate buffer solution (pH = 7.4), which presents excellent sensitivity, high selectivity, and reusability. Furthermore, the devised fluorescent probe in serum also exhibits the fluorescence “turn-off” process with a low detection limit of 0.279 μM, and the recovery rate of bilirubin is 99.20–101.9%. The possible mechanisms of the fluorescence “turn-off” process can be explained by resonance energy transfer, and the weak interaction between 1b and bilirubin.

A novel anionic Cd(ii)-based metal–organic framework was used toencapsulateLn(iii) ions, which exhibits tunable luminescence and selective sensing of bilirubin.     

Diphenyl polysulfides: cathodes with excellent lithiation performance and high specific energy for LSBs

Reversible lithium–sulfur batteries (LSBs) are considered one of the most promising next-generation energy storage systems. However, the shuttling effect of lithium polysulfide significantly weakens the electrochemical properties and the cycle life, hindering its practical application. Organo-sulfides are unique materials with low cost, profuse content and high capacity. Here, via quantum chemical calculations, we introduce a class of diphenyl polysulfides, PhS_nPh (2 ≤ n ≤ 15), which are all structurally stable, confirmed by calculation of their Gibbs free energies. The theoretical specific energy of PhS₁₅Ph is high, up to 2632 W h kg⁻¹, exceeding that of S₈. By calculating the bond dissociation energy of S–S in PhS_nPh molecules, we analyze the breaking processes of the S–S bonds in each step of lithiation. The microscopic mechanism of the fast reaction kinetics of PhS_nPh cathodes is explored. It is phenyl that prevents the formation of soluble long-chain polysulfide molecules (Li₂S₄, Li₂S₆, Li₂S₈) in the lithiation process, efficiently weakening the “shuttle effect”.

Reversible lithium–sulfur batteries (LSBs) are considered one of the most promising next-generation energy storage systems.     

Organic deliquescence: organic vapor-induced dissolution of molecular salts

This report demonstrates organic vapor-induced dissolution of several molecular salts (i.e., organic deliquescence), like water vapor-induced deliquescence. Systematic experiments indicate that appropriate organic deliquescent responses to volatile organic compounds can be designed according to the principle, “like dissolves like”. The phenomena will be useful for developing agents to collect various volatile organic compounds.

Several molecular salts exhibit organic deliquescence in response to organic vapors.

The importance of interactions between solid materials and gaseous molecules has recently been highlighted in the context of (i) CO_(g) adsorption or H₂ storage using metals,^1–8 (ii) vapor molecule detection in the environment,^9–17 and (iii) uptake and catalysis involving gaseous molecules, e.g., CO₂ reduction,^18–22 despite the limited interactions allowed by the extremely low density of gaseous molecules (∼10⁻³ times the density of liquids).Deliquescence is an essential phenomenon that relies on interactions between solid chemicals and water vapor;^23–25 specifically, solid chemicals absorb enough water vapor to become dissolved in an aqueous solution. This behavior has been observed as far back as ancient times when table salt containing nigari (magnesium chloride) hardened under high humidity. To date, deliquescence has been reported for various chemicals (e.g., citric acid, sodium hydroxide, potassium carbonate, magnesium chloride, calcium chloride), which capture water vapor from the atmosphere and spontaneously create aqueous solutions in humid conditions. For some water-soluble chemicals, simply increasing the environmental humidity can promote deliquescence (observed as the solid → liquid change) without heating or adding liquid. This phenomenon can be exploited to capture atmospheric water vapor, and calcium chloride (CaCl₂) has been employed as a chemical desiccant. However, to our knowledge, deliquescence involving organic vapor has not yet been reported, despite increased efforts to remove environmental volatile organic compounds (VOCs) in recent decades.^26–30 This may be because there are significantly lesser amounts of organic vapors in human living environments than there are water vapors in humid conditions. This report describes organic vapor-induced deliquescent phenomena involving several solid molecular salts that undergo solid → liquid changes in response to organic vapors. These changes were systematically investigated by varying the solid molecular salts and organic vapors in a closed system and confirmed to result from deliquescent phenomena, rather than melting (by heating) or dissolution (by adding liquid). Moreover, the organic vapor-induced deliquescence could be designed by considering the molecular structural relationship between the salt and the target organic vapor, thereby highlighting the generalizability of this behavior. Thus, deliquescent phenomena (previously believed to occur only with water vapor) were observed and designed with various organic vapors; these findings will be useful for treating environmental VOCs. Fig. 1a shows the setup for organic vapor exposure experiments (further details in the ESI^†). Briefly, ∼0.5 mg of powdered salt on a thin glass plate was placed onto blue cobalt glass, and 1.0 mL of organic solvent was divided among two small reservoirs in a 9 cm Petri dish. After isolating the system by adding a top glass cover sealed with grease, changes to the physical state of various salt powders were monitored under exposure to various organic vapors at room temperature. In a typical control experiment (i.e., water vapor-induced deliquescence of CaCl₂; Fig. S1 and Movie S1^†), the CaCl₂ powder clearly changed to an aqueous solution via deliquescence.Open in a separate windowFig. 1Organic deliquescence. (a) Experimental setup for organic vapor exposure in a sealed system. Organic deliquescent behaviors of (n-Bu₄N)PF₆ (b and c), NH₄PF₆ (d), and NH₄BF₄ (e) exposed to CHCl₃ (b) or DMF (c–e) (Movies S2–S5,^† respectively).First, we evaluated the deliquescence of tetrabutylammonium hexafluorophosphate ((n-Bu₄N)PF₆), which is a common organic salt that is soluble in organic solvents and widely used as an electrolyte in electrochemical experiments. When chloroform (CHCl₃) widely used as a solvent in chemical industry was employed as the organic solvent, the (n-Bu₄N)PF₆ powder gradually changed to liquid, while the amount of CHCl₃ in the Petri dish reservoirs decreased (Fig. 1b and Movie S2^†). This solid → liquid change was similar to the water vapor-induced CaCl₂ deliquescence under analogous conditions. After three hours of CHCl₃ vapor exposure, the entire area around (n-Bu₄N)PF₆ became liquid, and its weight increased by 1.8 times, thus confirming that the solid → liquid change was not caused by melting. These results were highly reproducible (p < 0.05), although the phase-change initiation depended on the experimental conditions (e.g., crystal size, organic solvent surface area). Thus, CHCl₃ was transferred from the reservoirs to the (n-Bu₄N)PF₆ powder, allowing (n-Bu₄N)PF₆ to dissolve in CHCl₃ owing to its high solubility (0.64 g (n-Bu₄N)PF₆ can be dissolved in 1.0 g CHCl₃ at 20 °C). These results confirmed that deliquescent phenomena could be induced by an organic solvent (organic deliquescence). However, such organic deliquescence was not observed for inorganic salts that were insoluble in CHCl₃ (e.g., ammonium hexafluorophosphate (NH₄PF₆), ammonium tetrafluoroborate (NH₄BF₄), sodium chloride (NaCl)).Next, analogous experiments were performed using N,N-dimethylformamide (DMF), which is used in large quantity for wet spinning and is a common polar organic solvent that can dissolve various types of salts. With DMF (Fig. 1c–e and Movies S3–S5^†), solid → liquid changes were observed for organic ((n-Bu₄N)PF₆) and some inorganic salts (NH₄PF₆ and NH₄BF₄), but not for NaCl and not for any salts without DMF (example control experiments with NH₄PF₆ shown in Fig. S2^†). After three hours of DMF vapor exposure, the weights of the salt components increased by 3.1, 6.9, and 7.2 times for (n-Bu₄N)PF₆, NH₄PF₆, and NH₄BF₄, respectively. Repeated experiments showed that p < 0.05 for the solid → liquid change of (n-Bu₄N)PF₆, and the sample weight of (n-Bu₄N)PF₆ under DMF vapor exposure was monitored over time by constructing a closed system in an analytical balance. The DMF vapor concentration was also monitored with a VOC monitor connected to the closed system. When the DMF vapor concentration exceeded ∼4 × 10³ ppm (∼0.4 kPa), the solid → liquid change was initiated (Movie S6^†). Then, the sample weight clearly increased after the DMF vapor concentration reached ∼5 × 10³ ppm (∼0.5 kPa) corresponding to the saturation vapor pressure.^31–33 Therefore, the observed phenomena were also attributed to organic deliquescence. To clarify the differences between the tested molecular salts, their solubilities in DMF were determined: 1.27 g (n-Bu₄N)PF₆, 1.07 g NH₄PF₆, or 0.29 g NH₄BF₄ could be dissolved in 1.0 g DMF at 20 °C, whereas NaCl was insoluble in DMF. In general, organic deliquescent phenomena were observed with organic and inorganic ammonium salts that were soluble in the target organic solvent. When using a polar organic solvent (DMF), the amount of transferred (i.e., collected) solvent was much greater than the amount of salt. This is an important feature of organic deliquescence, compared with conventional adsorption phenomena. To evaluate organic deliquescence by non-ammonium salts, similar experiments were performed using tetraphenylphosphonium bromide ((Ph₄P)Br) with CHCl₃ (solubility = 0.29 g g⁻¹) or DMF (solubility = 0.25 g g⁻¹) at 20 °C; solid → liquid changes were observed in both cases (Fig. 2a, b and Movies S7, S8^†). After three hours of vapor exposure, the weight of the (Ph₄P)Br component increased by 2.0 or 1.7 times in the presence of CHCl₃ or DMF, respectively. Thus, organic deliquescent phenomena can occur with non-ammonium salts (e.g., (Ph₄P)Br) that are soluble in organic solvents.Open in a separate windowFig. 2Organic deliquescent behaviors of (Ph₄P)Br (a and b) and (n-Bu₄N)Bz (c and d) exposed to CHCl₃ (a and c), DMF (b), or toluene (d) (Movies S7–S9^†).The observed organic deliquescence involved three processes (Fig. 3): (i) the evaporation of pure organic solvent generates organic vapor, which adsorbs onto the surface of the salt powder; (ii) some salt dissolves, thereby creating a small amount of saturated organic solution on the powder surface; (iii) because the vapor pressure is depressed in the saturated organic solution, the continuous supply of organic vapor (from evaporation) is condensed into the organic solution, thus allowing further dissolution of the salt. This condensation cycle continues until the vapor pressure of the highly-concentrated organic solution becomes comparable to that of the atmosphere. Meanwhile, evaporation reduces the amount of organic solvent in the reservoirs, and the organic vapor is transferred and condensed, thus increasing the amount of liquid around the salt component. The choice of molecular salt and its solubility in organic solvents are crucial factors for promoting organic deliquescence because the vapor pressure depression of the highly-concentrated solution is proportional to the molar concentration (i.e., each salt molecule splits into a cation and an anion in solution, which increases ion molar concentrations and facilitates vapor pressure depression). Thus, organic deliquescence can occur with salts exhibiting high solubility in organic solvents.Open in a separate windowFig. 3Proposed mechanism of organic deliquescence.Toluene used as a paint solvent is an important VOC whose emissions should be reduced; however, none of the aforementioned salts (i.e., (n-Bu₄N)PF₆, NH₄PF₆, NH₄BF₄, (Ph₄P)Br, NaCl) exhibited organic deliquescence or solubility in non-polar toluene. Instead, based on the general rule that “like dissolves like”, tetrabutylammonium benzoic acid ((n-Bu₄N)Bz) was used, owing to its superior solubility in toluene (2.42 g (n-Bu₄N)Bz in 1.0 g toluene at 20 °C). A solid → liquid change was observed when using (n-Bu₄N)Bz and toluene as the salt and organic solvent, respectively (Fig. 2d and Movie S9^†), and no change was noted in the absence of toluene (Fig. S3^†). After three hours of toluene vapor exposure, the weight of the (n-Bu₄N)Bz component increased by 1.1 times, which indicated organic deliquescence. These results confirm that (n-Bu₄N)Bz is suitable for organic deliquescence of toluene. The (n-Bu₄N)Bz salt also exhibited high solubility in CHCl₃ (2.06 g g⁻¹) and DMF (1.64 g g⁻¹), which enabled organic deliquescence in the presence of CHCl₃ (Fig. 2c and Movie S10^†) and DMF vapors (Fig. S3^†). After three hours of vapor exposure, the weight of the (n-Bu₄N)Bz component increased by 1.1 or 3.9 times when using CHCl₃ or DMF solvents, respectively.In summary, this report elucidates the solid → liquid changes of molecular salts in response to organic vapors and provides the first experimental demonstration of organic vapor-induced deliquescence by systematically investigating various salts and organic solvents. In contrast to water vapor-induced deliquescence by common chemicals under humid conditions, organic deliquescence had not been observed because of the low concentrations of atmospheric VOCs in human living environments. The results presented herein indicate that organic deliquescence is not unusual, but rather, organic deliquescent systems can be designed to target specific solvents based on the general rule that “like dissolves like”. Considering the success of CaCl₂ as a chemical desiccant to capture atmospheric water vapor and the urgent need to remove large volumes of VOCs from facilities using organic solvents,^26–30 organic deliquescence represents a promising approach for developing agents to collect VOCs.     

Dispersion-induced structural preference in the ultrafast dynamics of diphenyl ether

Dispersion interactions are omnipresent in large aromatic systems and influence the dynamics as intermolecular forces. The structural preference induced by dispersion interactions is demonstrated to influence the excited state dynamics of diphenyl ether (DPE) using femtosecond time-resolved transient absorption (TA) associated with quantum chemical calculations. The experimental results in aprotic solvents show that the S₁ state is populated upon irradiation at 267 nm with excess vibrational energy dissipating to solvent molecules in several picoseconds, and then decays via internal conversion (IC) within 50 ps as well as intersystem crossing (ISC) and fluorescence with a lifetime of nanoseconds. The polarity of the solvent disturbs the excited state energies and enhances the energy barriers of the ISC channel. Furthermore, the intermolecular dispersion interactions with protic solvents result in the OH–π isomer dominating in methanol and the OH–O isomer is slightly preferred in t-butanol in the ground state. The hydrogen bonded isomer measurements show an additional change from OH–O to OH–π geometry in the first 1 ps besides the relaxation processes in aprotic solvents. The time constants measured in the TA spectra suggest that the OH–O isomer facilitates IC. The results show that the OH–π isomer has a more rigid structure and a higher barrier for IC, making it harder to reach the geometric conical intersection through conformer rearrangement. This work enables us to have a good knowledge of how the structural preference induced by dispersion interactions affects excited state dynamics of the heteroaromatic compounds.

Dispersion interactions are omnipresent in large aromatic systems and influence the dynamics as intermolecular forces.     

Synthesis and pH-stimuli responsive research of gemini amine-oxide surfactants containing amides

The series of gemini amine-oxide surfactants with the formula C_nH_2n+1CONH(CH₂)₂N⁺O⁻(CH₃)–(CH₂)₃–(CH₃)N⁺O⁻(CH₂)₂NHCOC_nH_2n+1 (n = 11, 13, 15, and 17) has been synthesized successfully. Their isoelectric point and acid dissociation constant were measured to determine the ionization form of the surfactant molecules in aqueous solution within different pH values. The studies showed that the length of the hydrophobic alkyl chains had a great influence on the pH-stimuli responsive behavior of these surfactants. When n ≤ 13 (n-3-n-OA), the regularity of the pH-stimuli responsive behavior of the surfactant solutions was relatively consistent, while the surfactants with longer hydrophobic alkyl chain lengths lost this regularity (n ≥ 15). In addition, vesicles were observed in most of these surfactant aqueous solutions, with the exception of 11-3-11-OA. Moreover, the obvious flocculation phenomenon was observed within the range of pH 4–5, and they flocculated rapidly when they approached their isoelectric points. This process was reversible, which brought more possibilities for their application in drug delivery and release.

The series of gemini amine-oxide surfactants with the formula C_nH_2n+1CONH(CH₂)₂N⁺O^–(CH₃)–(CH₂)₃–(CH₃)N⁺O^– (CH₂)₂NHCOC_nH_2n+1 (n = 11, 13, 15, and 17) have been synthesized, and their pH-stimuli responsive behavior in aqueous solution has been studied.